[R-390] Off Topic - Transistor R390A sounding good.

[Bob Camp]

Hi

About all I can figure out is that different tubes overload in 
different ways. The guys I sell stuff to are all guitar amp people. 
They worry about what happens when they go into overload. About all I 
can say is that they can spot the "good" tubes in blind tests (I swap 
them and they tell me which one is best).

I would *think* we would have the same issue with front end tubes on a 
390. If it's a significant issue we should be able figure out what the 
best front end tubes are. I think I have a couple hundred in stock. 
Time to prove they are the best ....

	Take Care!

		Bob Camp
		KB8TQ


On Jan 1, 2005, at 1:36 PM, David C. Hallam wrote:

> Along these lines, can anyone explain for me why the audio people are
> willing to pay prices that approach or exceed $100 for specific tubes 
> that
> are versions of garden variety tubes, i.e., 12AX7, 12AU7, 6SN7, etc.  
> What
> was done to these tubes that make them special or is it just the 
> oxygen free
> copper speaker wire all over again?
>
> David C. Hallam
> KC2JD
>
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net 
> [mailto:r-390-bounces at mailman.qth.net]On
> Behalf Of Bob Camp
> Sent: Saturday, January 01, 2005 1:15 PM
> To: Charles B; R-390 HF Receiver List
> Subject: Re: [R-390] Off Topic - Transistor R390A sounding good.
>
> Hi
>
> One of the more interesting mysteries of the world is the enormous
> number of transistor part numbers out there compared to the number of
> tubes. If you look at a tube manual from the R390 era you will find
> roughly 1/100 the number of tubes compared to the number of transistors
> and diodes in an equivalent solid state book these days.
>
> We don't worry to much about a particular brand of tubes in the 390 but
> the audio guys go a bit nuts on specific manufacturers of "classic"
> tubes. As far as I can see the R390 approach (don't sweat it) works
> just fine except when you have a tube that's just plain bad. I have
> never seen a problem that always happens with a specific brand of tube
> in a 390.
>
> If you look in your 390 there are a bunch of fundamentally different
> tubes in it. You are not going to swap a dual triode for a pentode and
> have much success. Even if you stick to triodes they come in a wide
> variety of bias and gain setups.
>
> Bipolar transistors are different. You have two basic flavors NPN and
> PNP. Provided you don't run to much power, current or voltage do their
> thing ok. At a given current level the gain of most of them is very
> similar in a normal circuit.
>
> If you already have a bag full of diodes or transistors, try plugging
> one in and see what happens. It just may work and save you a major
> hassle.
>
> The Lankford SSB mod on the 390A is an very good example of this. There
> are probably thousands of diode part numbers that will work just fine
> in the circuit. They are easier to find by body style than by part
> number. If the diode looks like it will work it probably will.
>
> So if transistors are more like each other than tubes - why so many
> transistor types?
>
> Marketing rules ....
>
>
>         Take Care!
>
>                 Bob Camp
>                 KB8TQ
>
>
>
> On Jan 1, 2005, at 7:29 AM, Charles B wrote:
>
>> Hi all,
>> My R-390A is sounding good lately.
>>
>>
>> I don't know where to go for this info, so I am checking here?  I need
>> to replace a transistor.  I have gone to the
>> electronics store in West Palm Beach and they can't find it?
>> I checked with a source here on the web and it's not listed
>> in their catalog.  Anyway, if anyone could take a look
>> at the following number and let me know if they can
>> cross reference it, I'd appreciate it?  You can
>> get me off group at my email address of:
>>
>> ka4prf at us-it.net
>>
>> The transistor's number is     MPS 6530
>> I think the case has a large "E" on it?  The
>> resistor is an NPN type. O18 case
>> Thanks
>>
>> Chuck
>>
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